1. Field of the Invention
The present invention relates to a test apparatus, and a test method for performing an acoustic test for acoustic correction, and a compute program performed by the test apparatus.
2. Description of the Related Art
When listeners listen to audio signals replayed by a multi-channel audio system through a plurality of speakers, an acoustic field of the sound changes in response to a change in the structure of a listening room, the balance and sound quality in response to an listening environment such as a structure of a listening room, and a listening position of each listener with respect to the speakers. Depending on the listening environment, the listener at the listening position is unable to listen to sounds from the speakers in an appropriate acoustic field.
Such a problem is pronounced in a compartment of an automobile. Since the listening position of the listener is generally limited to a seat position in the automobile compartment, a distance permitted between each of speakers and the listener is typically limited to within a certain range. In such an environment, the balance of the acoustic field is significantly destroyed due to a time difference in arrival time of sounds from speakers. The compartment of the automobile is a relatively small closed space, and reflected sounds are scrambled in a complex manner and then reach the listener, thereby disturbing a desired acoustic field. The limitation imposed on the mounting position of the speakers rarely allows a sound to directly reach the ears of the listener. This factor causes a change in sound quality, thereby significantly affecting the acoustic field.
An acoustic correction technique is known to produce an acoustic field of an original sound source as faithful as possible under a listening environment of an audio system. Predetermined signal processing is performed in the audio signal to be outputted from the speaker. For example, a delay time is adjusted to correct a time difference between sounds reaching the ears of the listener. Also, an equalization correction is performed to correct, in sound quality and listening level of the sounds, a change in the sounds reaching the ears of the listener.
To efficiently perform the acoustic correction, the audio system preferably performs an automatic adjustment instead of a listener's manual adjustment depending on the listener's acoustic sense.
An acoustic correction apparatus measures acoustic characteristics of a listening environment, and sets a signal process parameter for acoustic correction on an audio output line of the audio system. If the audio signal processed in accordance with the set parameter is outputted from the speakers, a sound is enjoyed in an excellent audio field adaptively corrected to the listening environment without the need for the listener's acoustic manual adjustment.
The acoustic characteristics are measured as below as disclosed in Japanese Unexamined Patent Application Publication No. 2001-346299, for example. Microphones are placed at a listening position corresponding to the position of the ears of the listener. The acoustic correction apparatus causes a speaker to output a test sound, the outputted test sound is picked up by the microphone, and the picked up test sound is sampled. The acoustic correction apparatus determines a signal processing parameter for acoustic correction based on the results of a frequency analysis process performed on the sampled sound.
A pink noise is typically used to measure the test sound. During test, the listener hears the noise sound. The noise sound is far from comfortable to the listener.